1. Field of the Invention
The present invention is directed to a method of manufacturing microscopically small metal or metal alloy structures particularly for manufacturing structures used in a memory for cylindrical magnetic domains which memory has manipulation patterns, domain extenders, detectors, guide loop generators, domain annihilators, control lines and read lines disposed on a storage layer.
2. Prior Art
In devices such as memories involving cylindrical magnetic domains generally called bubbles, the coating width of the structure for example a magnetostriction-free Ni-Fe structure for the manipulation patterns of the cylindrical magnetic domains is approximately 3 to 20 .mu.m. Thus, it is extremely difficult in these devices to use photo-etching procedures due to problems of keeping undercutting during the etching step sufficiently small so that the lateral errosion of the structure in the zones protected by the photo-resist is sufficiently small. In order to avoid these difficulties, several different methods have been suggested and these methods are described in the following articles: V. Sadagopan, H. Hatzakis, K. Y. Ahn, T. S. Plaskett and L. L. Rosier, "High-Density Bubble Domain Shift Register" AIP Conference Proceedings, No. 5, 1971, pages 215-219; E. G. Spencer, P. H. Schmidt and R. F. Fischer, "Microstructure Arrays Produced by Ion Milling", Applied Physics Letters, vol. 17, No. 8, Oct. 15, 1970, pages 328-332; and J. P. Reekstin, "Fabrication of `Bubble` --Propagating Circuits by Electroless Deposition of Nickel-Cobalt-Phosphorous", Journal of Applied Physics, vol. b 42, No. 4, Mar. 15, 1971, pages 1362-1363. In addition, my United States Letters Patent No. 3,901,770 discusses a process for overcoming the problems of forming microscopically small structures. In this patent, it is suggested that a thin metal or metal alloy layer be vapor deposited on a carrier such as a glass carrier to a thickness of approximately 300 A. In the area of the cylindrical magnetic domain transport, a photo-resist layer is applied onto the metal layer. Channels corresponding to the desired metal or metal alloy structure are formed in the photo-resist layer in accordance to known methods such as photolithography to expose portion of the metal or metal alloy layer. A thin gold layer is then galvanically deposited on the exposed metal or metal layer and a thicker metal or metal alloy is then galvanically deposited on the gold layer with a second gold layer deposited on the metal alloy layer. After removing the photo-resist layer, the underlying thin metal film is removed. Preferably, the metal layer was a Ni-Fe layer and the removing was accomplished by etching the exposed Ni-Fe layer by dipping the coated carrier into a weak acid gold bath wherein the vapor deposited Ni-Fe layer is removed and replaced by a gold layer which gold layer is subsequently removed by etching with a known gold etching agent, for example, a diluted KCN solution. The process described in this patent is easy to carry out procedure and produces very great edge sharpness or border resolution for the structure being formed. In addition, the dimensions of the structure are not significantly influenced by the etching effects, for example undercutting during the etching process.